highcharts
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JavaScript charting framework
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JavaScript
/* *
*
* Equal Earth projection, an equal-area projection designed to minimize
* distortion and remain pleasing to the eye.
*
* Invented by Bojan Šavrič, Bernhard Jenny, and Tom Patterson in 2018. It is
* inspired by the widely used Robinson projection.
*
* */
;
/* *
*
* Constants
*
* */
const A1 = 1.340264, A2 = -0.081106, A3 = 0.000893, A4 = 0.003796, M = Math.sqrt(3) / 2.0, scale = 74.03120656864502;
/* *
*
* Class
*
* */
class EqualEarth {
constructor() {
/* *
*
* Properties
*
* */
this.bounds = {
x1: -200.37508342789243,
x2: 200.37508342789243,
y1: -97.52595454902263,
y2: 97.52595454902263
};
}
/* *
*
* Functions
*
* */
forward(lonLat) {
const d = Math.PI / 180, paramLat = Math.asin(M * Math.sin(lonLat[1] * d)), paramLatSq = paramLat * paramLat, paramLatPow6 = paramLatSq * paramLatSq * paramLatSq;
const x = lonLat[0] * d * Math.cos(paramLat) * scale /
(M * (A1 +
3 * A2 * paramLatSq +
paramLatPow6 * (7 * A3 + 9 * A4 * paramLatSq))), y = paramLat * scale * (A1 + A2 * paramLatSq + paramLatPow6 * (A3 + A4 * paramLatSq));
return [x, y];
}
inverse(xy) {
const x = xy[0] / scale, y = xy[1] / scale, d = 180 / Math.PI, epsilon = 1e-9;
let paramLat = y, paramLatSq, paramLatPow6, fy, fpy, dlat;
for (let i = 0; i < 12; ++i) {
paramLatSq = paramLat * paramLat;
paramLatPow6 = paramLatSq * paramLatSq * paramLatSq;
fy = paramLat * (A1 + A2 * paramLatSq + paramLatPow6 * (A3 + A4 * paramLatSq)) - y;
fpy = A1 + 3 * A2 * paramLatSq + paramLatPow6 * (7 * A3 + 9 * A4 * paramLatSq);
paramLat -= dlat = fy / fpy;
if (Math.abs(dlat) < epsilon) {
break;
}
}
paramLatSq = paramLat * paramLat;
paramLatPow6 = paramLatSq * paramLatSq * paramLatSq;
const lon = d * M * x * (A1 + 3 * A2 * paramLatSq + paramLatPow6 *
(7 * A3 + 9 * A4 * paramLatSq)) / Math.cos(paramLat), lat = d * Math.asin(Math.sin(paramLat) / M);
// If lons are beyond the border of a map -> resolve via break
if (Math.abs(lon) > 180) {
return [NaN, NaN];
}
return [lon, lat];
}
}
/* *
*
* Default Export
*
* */
export default EqualEarth;